Variable resistor



Nov. 1, 1960 w. A. BARDEN VARIABLE RESISTOR Filed Aug. 31, 1959 2Sheets-Sheet 1 INSULATING COATING;

Nov. 1, 1960 w. A. BARDEN VARIABLE RESISTOR 2 Sheets-Sheet 2 Filed Aug.31, 1959 jmdwfw United States Patent VARIABLE RESISTOR Wayne A. Barden,Elkhart, Ind., assignor to CTS Corporation, Elkhart, Ind., a corporationof Indiana Filed Aug. 31, 1959, Ser. No. 837,269

14 Claims. (Cl. 338-174) This invention relates to variable resistorsofthe type employed in radio and television receivers and has as itspurpose and object to increase the load carrying capacity of suchresistors without increasing the size thereof or adding to its cost. I

More specifically, it is an object of this invention to provide avariable resistor in which the base or substrate which carries theresistance path is of metal instead of the customary insulatingmaterial, so that heat generated when the resistor is under electricalload will be uniformly and rapidly conducted to all parts of the baseand thence dissipated.

' this invention pertains, the base of the stator element is With theabove and other objects in viev which will appear as the descriptionproceeds, this invention resides in the novel construction, combinationand arrangement of parts substantially as hereinafter described and moreparticularly defined by the appended claims, it being understood thatsuch changes in the precise embodiment of the hereindisclosed inventionmay be made as come within the scope of the claims.

The accompanying drawings illustrate one complete example of thephysical embodiment of the invention, constructed according to the bestmode so far devised for the practical application of the principlesthereof, and in which:

Figure 1 is a longitudinal sectional view through a varie able resistorembodying this invention;

Figure 2 is an end view of the resistor with its cover removed and withparts thereof broken away to better illustrate structural details;

Figure 3 is a fragmentary sectional view taken through Figure 2 on theplane of the line 3-3; and

Figure 4 is an exploded perspective view of those parts of the statorelement of the variable resistor, with which the invention is primarilyconcerned, the parts of the stator element not shown being theresistance element, the collector ring or contact, and the terminals forboth.

Referring now particularly to the accompanying drawings, in which likenumerals designate like parts, the numeral 3 designates generally thestator element of the variable resistor which, together with a rotorelement 4 and a cover 5 constitutes the entire unit.

The rotor element 4 is conventional and comprises the customary bridgingcontactor 6 with its spring fingers 7 and 8 respectively bearing uponthe resistance element 9 and the collector ring or center contact 10 ofthe stator element to traverse the same as the resistor is adjusted. Thebridging contactor 6 is carried by a drive arm 11 which, together with astop plate 12, is fixed to the shaft 13 of the rotor. The stop plate 12has the usual limit stop 14 which travels in an orbit to collide with astationary stop 15' on the cover and thereby defines the limits .ofrotation of the rotor element.

The shaft 13 of the rotor element is journalled in a thimble or bushing16 which serves to tie the rest of the stator elements together, andalso provides means for mounting the resistor upon a panel, not shown.

Ordinarily, in variable resistors of the type to which made ofinsulating material. Here it is a circular, generally flat metal disc17. The marginal or peripheral portion 18 of this disc is fiat and hasthe means which provides the resistance path, i.e. the resistanceelement 9 or its equivalent, mounted thereon, but insulated therefrom bya thin coat 19 of insulation, such as varnish. It is significant andimportant that the resistance path is separated from the metal base 17only by this thin coat or layer of insulation, and it is this featurewhich is primarily responsible for the improved heat dissipationachieved by this invention.

A segment of the fiat peripheral portion 18 of the disc 17 is cut awayto form an interruption 20 which is occupied by the outer sector shapedpart 21 of a terminal board 22. The inner part 23 of the terminal boardis circular and is received within a central depression 24 in the base17. This depression has a flat bottom 25 and a sloping sidewall 26, andis of such depth that with the underside of the terminal board restingon the bottom 25, the top face of the terminal board is flush with theinsulation coated surface of the peripheral portion 18. Aligned holes 28and 29 at the center of the base 17 and the circular inner part 23 ofthe terminal board receive one end portion 30 of the thinrble or bushing16.

The segment-shaped interruption 20 has opposite side edges 31 which areparallel to one another and lie in planes equidistant from the axis ofthe hole 28. These edges 31 have a locating function for a purpose to bedescribed, and the fact that they are parallel to one another issignificant.

The edges 31 connect with diagonal edge portions 32 which extend acrossthe sloping wall 26 and, as shown in Figure 2, are substantially radialto the axis of the hole 28. The inner ends of the diagonal edge portions32 terminate at the junction of the fiat bottom wall 25 and the slopingwall 26 of the central depression 24, and between these points theinterruption 20 is bounded by a continuation of the circumference of thecircular bottom 25 of the depression. Here a flange 33 projects downfrom the bottom wall 25 for a purpose to be described.

The outer ends of the diagonal edge portions 32 extend across flanges 34bent down from the ends of the arcuate peripheral portion 18. Since thejunctions of the flanges 34 with the peripheral portion 18 are gentlyrounded, the insulating coating 19 may extend unbrokenly thereover.

The terminal board 22 is stamped from insulating material, such asBakelite or fibreglass and, by virtue of its particular shape andthickness, its entire top surface is flush with the insulation coatedfiat surface of the peripheral portion 18. Accordingly, the resistanceelement which lies upon the insulated fiat surface of the peripheralportion and the collector contact which lies upon the center portion ofthe terminal board are substantially coplanar.

At the junction of its circular inner part and sectorshaped outer part,the terminal board has parallel side edges 36 equispaced from a plane ofsymmetry passing perpendicularly through the terminal board andcontaining the axis of its hole 29. These side edges 36 engage thelocating edges 31 on the base to hold the terminal board againstrotation with respect to the base. Since the side edges 36 are spacedapart just slightly less than the distance between the locating edges 31of the base, they have snug engagement therewith, and because of theparallel disposition of the edges 31 and 36, the terminal board issecure against turning about its connection with the base, despite anypossible radial misalignment between these parts.

At the opposite side of the base is a ground plate 40. This groundplate, like the base, is stamped from sheet down-turned flange 33 at thebottom of the segment-like interruption or cutout in the base receivedin a correspondingly placed notch 44 in the bottom of the cutout 43.

Thimble locating protrusions 45 project from the outer face of theground plate to receive opposite corners of a hexagonal flange 46 on thethimble or bushing, and hold the latter against turning, and thusgenerally assist in the assembly of the unit, in which condition theflange 33 engages the adjacent flat face of the hexagonal flange.

Theground plate also has a pair of diametrically opposite lugs 47projecting therefrom to engage in apertures in 'a panel (not shown) uponwhich the unit may be mounted to hold the same against turning, it beingunderstood that a clamping nut (not shown) is threaded onto the thimbleor bushing to secure the unit to the panel.

The central depressed portion 41 of the ground plate has a hole 48 atits center, which, like the holes 28 and 29 in the base and terminalboard, receives the adjacent end portion 30 of the thimble or bushing.The ground plate, base and terminal board are held in their assembledrelationship by being clamped between the hexagonal flange 46 againstwhich the ground plate bears, and the rolled over edge 50 of the thimbleportion 30.

heat generated in the resistance element when the unit is underelectrical load, will be quickly conducted to and uniformly distributedin the metal base and ground plate and, thence, dissipated. Hot spotswhich are due to high resistance radiants are thus eliminated and, inaddition, the resistor can easily handle loads that would seriouslyoverload a comparable sized variable resistor having the conventionalbase of insulating material.

Other features of the disclosed and described construction contribute tothe fulfillment of this main objective of the invention. Thus, theprovision of the downturned flanges 34 at the ends of the arcuateperipheral portion 18, enable the insulating varnish or coat to extendover the flanges and. thereby assure against the presence of uninsulatededge portions of the base directly contiguous to the resistance element.While the locating edges 31 of the base may not be coated with varnish,they are covered by the adjacent locating edges 36 of the terminalboard.

Another feature of the described and illustrated structure whichcontributes toward the overall improvement gained by this invention, isthe parallel disposition of the engaging locating edges 31 and 36; Ascan no doubt be appreciated in production the assembly of the parts mayresult in some slight radial displacement between the terminal board andthe base; and since the ends of the resistance element are secured tothe terminal board,

' relative rotation between the terminal board and base The arcuatelength of the resistance element 9 is greater than that of the arcuateperipheral portion 18 of the base which it overlies. Hence, the endportions of the resistance element extend into the segment-likeinterruption 20 and overlie the adjacent portion of the terminal board,to which they are clamped by terminals 51. The terminals 51 are securedto the terminal board by rivets 52 which pass through flat attachingportions 53 of the terminals, through radially projecting low resistanceterminal portions 54 on the ends of the resistance element, and throughthe terminal board. The fiat attaching portions 53 of the terminals arethus tightly clamped against the low resistance terminal portions 54;and to secure the terminals against rotation about their attachingrivets, the terminals have tangs 55 which are received in notches 56 inthe side edges of the terminal board, and tongues 57 which are receivedin other notches 58 and are bent down and back to provide the terminalswith solder lugs 59.

The collector ring or contact 10, as already noted, overlies and issupported upon the circular inner part 23 of the terminal board, whereit is held by the reception of part of it's terminal 60 in a slot 61 inthe terminal board, and another part 62 thereof in a notch 63, the part62 being extended to provide the solder lug 64 for the collectorcontact. Of course, the center Contact or collector ring is also held inplace by the contact pressure of the fingers 8 of the bridging contactorriding thereon, it being understood that the rotor element of thecontrol is secured against rearward axial displacement in anyconventional manner, as by a C-washer 66 snapped onto the shaft 13 andbearing against the front end of the thimble or bushing 16.

The cover 5 has the conventional stamped sheet metal construction,cup-shaped as shown, with tangs extending from its edge to be receivedbetween segments 70 projecting from the edge of the base 17, and thenclinched over the front of the 'ground'plate.

From the foregoing description taken in connection with the accompanyingdrawings, it will be apparent to those skilled in the art that thevariable resistor of this invention possesses several important andsignificant advantages. First and foremost is the fact that, since thebase is of metal, and is spaced from the resistance ele- "ment only bythe'thin coat of insulation on the. base, all

must be prevented. By having the edges 31 and 36, or at least one ofthese edges, i.e. either the edges 31 or the edges 36 parallel to oneanother, as shown and described, it follows that the desired securityagainst relative rotation is achieved, despite any possible radialmisalignment between the terminal board and base.

What is claimed as my invention is:

1. A variable resistor having cooperating stator and rotor elements, theformer comprising a substantially flat base, and means providing anarcuate resistance path and a collector contact concentric with theresistance path at one side of the base, and the latter comprising abridging contactor having contact fingers bearing on the resistance pathand on the collector contact and means to rotate the bridging contactor,the resistor being characterized: by the fact that the base is agenerally circular metal disc having a peripheral portion with a fiatsurface at the side of the base at which the resistance path andcollector contact are located, the disc having a notch in its peripheryforming an interruption in its peripheral portion; a terminal board ofinsulating material filling said interruption and having a flat surfacewhich is flush with said flat surface of therperipheral portion; a thincoat of insulation on said flat surface of the peripheral portion; themeans providing the resistance path overlying said flat surface of theperipheral portion and being spaced therefrom solely by said coat ofinsulation, and the end portions of the resistance path extending ontothe adjacent flat surface of the terminal board; and terminals for theends of the resistance path fixed to the terminal board.

2. The variable resistor of claim 1, further characterized by the factthat the terminal board has an inner portion overlying the centralportion of the metal disc; and rivet means passing through the center ofthe metal disc and said inner portion of the terminal board securingsaid parts together.

3. The variable'resistor of claim 2, further character- 'ized by thefact that the central portion of the metal disc inside :its flatsurfaced peripheral portion is depressed beneath the plane of its fiatsurface; by the fact that the inner portion of the terminal board isnested within said depressed central portion of the disc; and by thefact that the peripheral portion of the disc has spaced apart locatingedges between which the adjacent portion bf the terminal board is snuglyreceived to Secure the terminal board and the disc against relativerotation.

' 4. The variable resistor of claim 3 further characterized by the factthat the locating edges on the said peripheral portion of the disc areparallel to and equispaced from a plane containing the axis of the rivetmeans, so that despite radial misalignment between the disc and theterminal board occasioned by production tolerances, said parts are heldagainst relative rotation.

5. A variable resistor having cooperating stator and rotor elements, theformer comprising a substantially flat base, and means providing anarcuate resistance path and a collector contact concentric with theresistance path at one side of the base, and the latter comprising abridging contactor having contact fingers bearing on the resistance pathand on the collector contact and means to rotate the bridging contactor,the resistor being characterized: by the fact that the base is agenerally circular metal disc having a flat peripheral portion uponwhich the resistance path is located and a central portion depressedbeneath the plane of the surface of the peripheral portion at which theresistance path is located, the peripheral portion being cut away forpart of its circumferential extent to provide an interruption therein; aterminal board of insulating material having an inner part seated in thedepressed central portion of the disc and an outer part received in andfilling said interruption, said terminal board having a thicknesssubstantially equal to the extent the central portion is depressedbeneath the plane of said surface of the flat peripheral portion so thatone face of the terminal board is substantially flush with said surfaceof the flat peripheral portion; a thin layer of insulation between saidsurface of the peripheral portion of the disc and the means providingthe resistance path directly contiguous to both so that the meansproviding the resistance path is separated from the metal disc only bysaid insulation, and the end portions of the resistance path extendingonto the adjacent surface of the terminal board; and terminals for theends of the resistance path and for the collector contact carried by theterminal board.

6. A variable resistor having exceptional heat dissipating ability andcomprising: a base in the form of a substantially circular metal dischaving a peripheral flat faced portion which is interrupted by a notchextending generally radially into the disc; a thin coat of insulationcovering the flat face of said peripheral portion of the metal disc; aflat arcuate resistance element overlying the flat face of saidperipheral portion and directly contacting the coat of insulationthereon so that the only separation between the resistance element andthe metal disc is said coat of insulation, the end portions of theresistance element extending into said notch; means providing acollector contact concentrically disposed inside the arcuate resistanceelement; a terminal for the collector contact projecting substantiallyradially therefrom into said notch and between the ends of theresistance element; terminals for the ends of the resistance elementelectrically connected to the end portions thereof; and a rotatablebridging contaotor having contact fingers bearing upon the resistanceelement and the collector contact.

7. A variable resistor having cooperating stator and rotor elements, theformer comprising a substantially flat base, and means providing anarcuate resistance path and a collector contact concentric with theresistance path at one side of the base, and the latter comprising abridging contaotor having contact fingers bearing on the resistance pathand on the collector contact and means to rotate the bridging contaotor,the resistor being characterized: by the fact that the base is agenerally circular metal disc having a peripheral portion with a flatsurface at the side of the disc at which the resistance path andcollector contact are located, the disc having a notch in its peripheryforming an interruption in its peripheral portion, which notch ispartially defined by opposed spaced apart downturned flanges on the discthat extend transversely across the peripheral portion of the disc andmerge gradually and gently with the flat surface of the peripheralportion; a thin coat of insulation on said flat surface of theperipheral portion extending around the junction with and over saiddown-turned flanges; and the means forming the resistance path beingdirectly contiguous to said coat of insulation, so that the resistancepath overlies said flat surface of the peripheral portion and is spacedtherefrom only by the insulation, the end portions of the resistancepath extending beyond said down-turned flanges and into the notch; andterminal means for the ends of the resistance path.

8. The variable resistor of claim 7, further characterized by: the factthat the central portion of the disc is depressed beneath the plane ofsaid flat surface of the peripheral portion, and is connected with theperipheral portion by a sloping wall that circumscribes said centralportion and has an arcuate length less than that of said flat surface ofthe peripheral portion, the ends of said arcuately extending slopingwall being connected with the down-turned flanges by locating edgeportions of the notch; a terminal board having an inner part seated uponthe central depressed portion of the disc and an outer part received inthe notch, said outer part having a surface which is flush with saidflat surface of the peripheral portion, and the end pontions of theresistance path being on said fiat surface of the terminal board; theterminals for the ends of the resistance path being fixed to theterminal board; rivet means passing through the center of the disc andthe adjacent portion of the terminal board clamping said parts together;and the terminal board having opposite locating edges engaging saidlocating edges of the notch in the disc, to hold the terminal board andthe disc against relative rotation about the rivet means, at least thelocating edges on one of said two parts being parallel to one anotherand lying in planes which are equidistant from the axis of the rivetmeans.

9. The variable resistor of claim 8, further characterized by: a metalground plate generally conforming in size and shape to said disc andcontiguous to the side thereof opposite that at which the resistancepath and collector contact are located; the disc, ground plate and theinner part of the terminal board having aligned holes therein throughwhich the rivet means passes; the rivet means being a bushing havingshoulders bearing against the ground plate and the inner part of theterminal board; and the means for rotating the rotor element being ashaft journalled in the bushing.

10. The variable resistor of claim 9, further characterized by flangemeans on the disc engaging in a notch in the ground plate to secure saidparts against relative rotation.

11. The variable resistor of claim 10, further characterized bycooperating means on the ground plate and the bushing by which theentire unit may be secured to a supporting panel, and held againstrotation thereon about the bushing.

12. A variable resistor having cooperating stator and rotor elements,the former comprising a substantially flat base, means providing anarcuate resistance path with low resistance hop-offs at the ends thereofand a collector contact concentric with the resistance path at one sideof the base, and the latter comprising a bridging contactor havingcontact fingers bearing on the resistance path and the collector contactand means to rotate the bridging contaotor, the resistor beingcharacterized: by the fact that the base is a generally circular metaldisc having a central depression and an arcuate peripheral portion, thetop surface of which is substantially flat and at an elevation above thebottom of the depression, the central portion of the disc which formsthe bottom of the depression being substantially circular, and a curvedintervening wall joining the arcuate peripheral portion to the bottom ofthe depression, said curved wall extending around only part of thecircumference of the bottom of the depression and terminating short ofthe ends of the arcuate peripheral portion; a terminal board ofinsulating material having an inner part seated in the depression and anouter part bridging the space between the ends of the arcuate peripheralportion; means securing the terminal board to the metal disc; a thincoat of insulationon said substantially flat top surface of theperipheral portion; the means providing the resistance path overlyingsaid flat surface of the peripheral portion and being spaced therefromsolely by said coat of insulation, and the low resistance hop-ofis atthe ends of the resistance path overlying the terminal board; andterminals for the low resistance hop-offs fixed to the terminal board ingood electrical contact with the hop-offs.

13. The variable resistor :of claim 12, further characterized by thefact that the :ends of said curved intervening wall form locatingshoulders; and by the provisionrof abutments on the terminal boardengaging said locating shoulders to thereby establish a predeterminedpositional re lationship between the terminal board and the metal disc.

14. The variable resistor of claim 13, funther characterized by the factthat the inner portion of the terminal board and the bottom of thedepression have aligned centrally located holes; and by the fact thatthe means for securing the terminal board to the disc comprises a hubportion passing through said holes; and shoulders on the hub portionclamping the adjacent central portions of the terminal board and disctogether.

References Cited in the file of this patent UNITED STATES PATENTS

